Jan Koum. His name might be unknown to most, but this is the guy (along with his partner Brian Acton) who created and launched the WhatsApp messaging app, later to be sold to Facebook for a crazy $19 billion. His net worth is a great $7.9 billion!

Rags to riches: Co-founder of WhatsApp is suddenly worth $6.8bn

On Wednesday, as he announced Facebook’s record-breaking $19bn (£11.4bn) acquisition of the mobile messaging service WhatsApp, Mark Zuckerberg reflected that he had known WhatsApp’s chief executive, Jan Koum, “for a long time”. It is possible the pair met shortly before WhatsApp’s creation in 2009, when Mr Koum and his company’s co-founder Brian Acton both applied for jobs at Facebook – and were rejected.